1. Field of This Invention
This invention relates to separation devices by which gaseous mixtures, in particular mixtures of gaseous isotopes, can be separated into their components of different molecular mass.
2. Description of the Prior Art
Mass-dependent radial separation effects in thermal flows in the acceleration field are already being used for isotope separation in the so-called gas centrifuges. Typical gas centrifuge designs are described by K. Cohen and G. M. Murphy, "The Theory of Isotope Separation as Applied to the Large-scale Production of U.sup.235," New York, McGraw-Hill, (1951), p. 103 ff, and by R. Schutte, "Diffusionstrennverfahren", Ullmanns Enzyklopadie der Technischen Chemie, Fourth Ed., Vol. 2, Weinheim, Verlag Chemie, (1972), p. 630 ff.
The rotor of gas centrifuges is a hollow body into which the gas is introduced axially for separation. As a result of axial temperature differences, which are adjusted at the hollow body, the gas moves in a circulatory convective flow in the acceleration field of the rotating hollow body. The partially separated gas fractions are removed at two differently located outlets and fed to the other separation devices. The separation efficiency of these gas centrifuges is relatively low, particularly because the peripheral velocity is limited for reasons of material to about 700 m .multidot. s.sup.-1 (at a diameter of 400 mm, this corresponds to 600 revolutions per second). Construction of the centrifuges is extremely expensive; the material used must meet very high requirements.
H. Zeibig describes in his dissertation ["Isotopentrennung von Gasen durch Thermodiffusion mit einer in einem geschlossenen Gehaeuse rotierenden Scheibe," (trans.: Isotope Separation of Gases by Thermodiffusion Using a Disc Rotating in a Closed Casing), Technische Hochschule Aachen, (1966)] the radial separation effect at a smooth disc which is cooler than the casing. One of the drawbacks of this design is that the maximum separation effect is reached at speeds between 2 and 6 revolutions per second, so that only low acceleration fields can be used and the separation effect is relatively small.
It has also been suggested to make use of the different suction capacities of a trubomolecular pump for gases of different weight to reduce the partial pressure of the air in a helium-air mixture [W. Becker, "Erhochung der Empfindlichkeit des Helium-Lecksuchers durch Verwendung einer Turbomolekularpumpe besonderer Konstruktion," (trans.: Increasing the Sensitivity of a Helium Leak Detector by Using a Turbomolecular Pump of a Special Design), Vakuumtechnik, Vol. 17, (1968) pp. 203-205]. This method provides for the use of the turbomolecular pump at speeds of up to 270 rps for evacuating the mass spectrometer tube; the passage of helium in the direction opposite to the pumping direction is slightly impeded, i.e., that the passage has dimensions (diameter, wall distance) which are comparable or larger than the mean free path of helium at the applied pressure. An essential drawback of this method is the fact that the axle at the fore-vacuum flange of the turbomolecular pump has oil lubricated bearings, whereby the gas in that area is contaminated with oil vapor. With such device, the gas mixture can be separated to a substantial degree only if the components differ widely in molecular mass.